XCode 4.6 / Clang 4.2 can't find C++11 headers

I'm trying to include some C++11 headers in an iOS project, but XCode / Clang can't find them. I'm trying to include

<memory>

,

<functional>

and a few others. But it complains that it can't find them during the build (despite me right-clicking and "Jumping to definition" which loads the file...). How do I get my project to use C++11 header files?

It turned out that Clang's error message was unhelpful: the root include for these files was a .m file, compiling as Objective-C, so I renamed it to .mm, to compile as Objective-C++, and it started working.